Microwave-frequency ovens similar the type disclosed herein, and primarily used for thermal treatment of food-stuffs, are known in the art.
One prior-art microwave-frequency oven comprises an microwave-frequency electromagnetic oscillator connected through a slot-type exciter to a working chamber having a loading-unloading opening closed by a door. Installed inside the working chamber for the purpose of uniform heating of the product is a rotating frame carrying dielectric shelves onto which the products are placed for treatment.
A disadvantage of this known microwave-frequency cyclicaction oven is its low productivity, because loading and unloading of the products being treated require that the operation of the microwave-frequency oven be discontinued for that purpose, yet without switching off the oven it is impossible to prevent dissipation of microwave-frequency energy from the working chamber.
In addition, due to the short-time duration of the thermal treatment process, and the inconvenient loading and unloading of the products being treated, the oven utilization factor, i.e., ratio of the duration of thermal treatment versus the duration of the entire cycle (loading -- thermal treatment -- unloading) is very low. Because of the cyclic mode of operation of the microwave-frequency electromagnetic oscillator, the service life of the latter is considerably reduced.
The food-stuff thermal treatment process even under optimum conditions is also made more difficult.
Also known are microwave-frequency continuous-action ovens comprising a conveying device taking the form of a continuous band, or a chain to carry the products being treated. In order to prevent dissipation of microwave-frequency energy into the environmental space, these microwave-frequency ovens are provided with cut-off attenuators positioned at the conveying device inlet to, and the outlet from the working zone.
A disadvantage of this known microwave-frequency continuous oven is associated with its large size, and its use of a relatively large amount of metal to manufacture, as well as the unreliable operation of the cut-off attenuators with the resultant dissipation of microwave-frequency energy into the environmental space. Besides, in these microwave-frequency ovens, the sanitation of the conveying device carrying the product in the course of thermal treatment is rather difficult.